The present invention generally relates to resource allocation in a wireless communication network, and particularly relates to efficient resource allocation for user admission, such as at call origination or at hard handoff.
Finite communication resources constrain the number of mobile stations and other wireless communication devices (users) that may be supported within a given service area. For example, within a defined service area (cell), the typical Code Division Multiple Access (CDMA) network uses at least one “CDMA channel.” In this context, a CDMA channel represents the collection of forward and reverse communication links between the network and the users on a particular carrier frequency. Thus, the CDMA channel may be thought of as the “intersection” between a particular CDMA carrier and a particular cell.
On the forward link, the CDMA channel's capacity is constrained by, among other things, available transmit power and available spreading code resources. Users are added to the CDMA channel by allocating dynamically changing portions of the total forward link transmit power, and further by allocating one or more spreading codes to code-multiplex each user's individual traffic stream(s) onto the CDMA channel. Thus, the ability to allocate one or more “radio links” to a particular user on a particular CDMA channel depends on the availability of power and code resources for that channel.
Increasing the number of CDMA channels available within a particular cell substantially increases the number of users that can be supported within the cell. The use of multiple carrier frequencies enables the use of two or more CDMA channels within a particular cell. For example, the use of carrier frequencies F1 and F2 in a particular cell provides one CDMA channel in frequency F1 and another CDMA channel in frequency F2 for that cell. As a point of increased flexibility, not all cells necessarily offer multiple carrier frequencies. For example, certain cells, such as cells in a downtown urban area, may operate with two or more carrier frequencies, while outlying cells might operate with only one carrier frequency. Generally, the mix of single and multi-carrier cells within a plurality of cells may be tailored as needed or desired to meet capacity and connection reliability targets.
Even with the use of multiple carrier frequencies, the ability to efficiently utilize the added capacity and do so reliably from the perspective of network users requires a more intelligent approach to resource granting than exists in current multi-carrier networks. For example, conventional multi-carrier networks may perform limited inter-carrier load balancing such that users admitted into a particular cell are more or less assigned to the least loaded carrier frequency in that cell. However, since those users may be served in soft handoff from neighboring cells, the relative carrier frequency loading in that one cell may indicate little or nothing about the relative carrier frequency loading across the cells that will or might be used to support the mobile station.
Moreover, without considering the availability of radio links across multiple CDMA channels, the conventional networks forfeit the opportunity to increase service reliability by not granting resources on the carrier frequency that maximizes soft handoff for the mobile station or at least selecting the carrier frequency that satisfies a minimum soft handoff criterion. For these and other reasons that will become apparent, an improved method and apparatus are needed for granting resources to mobile stations in multi-carrier CDMA environments.